Field of Invention
The present invention relates to an electronic device in power electronic fields. More particularly, the present invention relates to an electronic device including a magnetic element.
Description of Related Art
With respect to a conventional transformer, a planar transformer uses the material such as a single-layer or multi-layer printed wiring board (PWB) or copper foil to replace copper wires in the conventional transformer. Wires in the planar transformer are actually a planar conductor, in which currents flow to its edges away form its center, but the currents still all flow through the planar conductor, and thus quite a high current density can be obtained. Further, because a magnetic core used in the planar transformer has a small volume, such that a large surface area, a flat profile, better heat dissipation could be achieved, and a better efficiency can be obtained. Furthermore, the planar transformer advantageously has a compact structure, better coupling and good insulation, etc., such that the planar transformer is suitable for product miniaturization, and has been applied to various products, such as a power converter.
Referring to FIG. 1, FIG. 1 is a schematic block diagram showing the circuit principle according to a power converter including a planar transformer.
As shown in FIG. 1, a power converter 1 includes a planar transformer 11, a secondary-side circuit module 12 and a primary-side circuit module 13. The secondary-side circuit module 12 is coupled to a secondary side of the planar transformer 11, and the primary-side circuit module 13 is coupled to a primary side of the planar transformer 11.
Further, referring to FIG. 2, FIG. 2 is a schematic structural diagram showing a power converter having a conventional planar transformer.
The planar transformer 11 includes a magnetic core and a winding (not shown), in which the secondary-side circuit module 12 is connected to the winding through a secondary-side outlet connector, and the primary-side circuit module 13 is connected to the winding through a primary-side outlet connector.
However, a current loop formed from a winding outlet connector of the conventional planar transformer 11 and an external circuit module of the conventional planar transformer 11 may store relatively large magnetic energy, and thus larger leakage inductance may be formed. For example, a loop formed from the secondary-side outlet connector of the winding and the secondary-side circuit module 12 may form larger leakage inductance. The leakage inductance is an important index for the planar transformer. For example, if the leakage inductance exists in a switching mode power supply, a counter electromotive force will be caused by the leakage inductance when a switch device is turned off instantaneously, in which the counter electromotive force is likely to cause an over voltage breakdown of the switch device. Further, the leakage inductance may form an oscillation circuit with distributed capacitors in the external circuit and the planar transformer windings; further generating oscillation and electromagnetic energy radiating outward, resulting in electromagnetic interference (EMI). Furthermore, as to some transformers, such as a flyback transformer, the leakage inductance will cause loss, thus lowering the efficiency of the flyback transformer.
In view of this, it is a technical problem to be solved by technical people in the industry regarding how to design a converter to reduce magnetic energy stored in a loop formed from an outlet connector of a planar transformer and an external circuit for reducing leakage inductance by changing the structure of the planar transformer.